To clean up our Changelog, this change modifies the use of
github-changelog-generator to only use PRs. This ensures
that our Changelog only reflects actual changes and makes
it easier for our users to see the actual changes made to
the codebase.
docs and www changes will be excluded from the Changelog as well.
The CHANGELOG.md will start from v1.21.0. All release prior to
v1.21.0 have been moved to HISTORICAL_CHANGELOG.md which will
remain static. Should we be able to bend github-changelog-generator
to our ways, I'll merge them back together at a future date.
Signed-off-by: Adam Leff <adam@leff.co>
